The Magic packet technology from AMD says, to wake up the computer
which is connected to a router; the Magic packet should be sent via
subnet-directed broadcast.
This is because router may not forward unicast packet to the sleeping
computer, "Router aging problem"

Now, I am thinking of a way to avoid this router aging as most routers
do not forward the subnet-directed broadcast.

How can avoid router aging? I understand, now the Magic packet
technology supported NIC will look for the Magic packet alone in sleep
mode.
what additional functions that I need to implement in NIC while sleep
mode to keep my sleeping computer known to the router? Is it just ARP
requests and reply?

any inputs on this front would be appreciated.